1. Field of the Invention
The present invention relates to a high-voltage field-effect transistor and to a method for manufacturing a high-voltage field-effect transistor.
2. Description of the Background Art
U.S. Pat. No. 5,698,869 discloses a semiconductor structure and the manufacture of a semiconductor structure, in which the leakage current is reduced and the breakdown voltage is increased for an insulated-gate transistor, such as a MOSFET. A semiconductor region with a reduced bandgap for silicon, such as SixGe1-x, SixSn1-x, or PbS, is formed in an interior area of a source region or a drain region of an SOI component. To effectively suppress the potential-free body effect in an SOI component, the SiGe region must be formed sufficiently close to a pn junction between the source region and a channel region. In order to reduce the influence of crystal imperfections by the germanium atoms, it is proposed to form the region with the reduced bandgap up to the channel region.
In Japanese patent No. 06013561 A, germanium is implanted into the source and drain region of a MOSFET, so that the bandgap in the source region and in the drain region is reduced to lower a current gain of a parasitic bipolar transistor. U.S. Pat. No. 6,765,247 B2 shows a similar situation. In Japanese patent No. 7335887 A, moreover, a horizontal concentration distribution of germanium is achieved in two steps of germanium implantation in a conventional LDD process.
U.S. Pat. No. 6,828,632 B2 relates to an SOI structure. A well region is formed above an oxide layer. The well region is applied epitaxially in several layers, whereby the layers have a silicon-germanium layer. The silicon-germanium layer has a number of recombination centers in the source/drain region.
U.S. Pat. No. 6,787,883 B1 discloses the preparation of a Si1-x,Gex layer in the channel region, which forms a Si1-xGex—Si heterojunction to the substrate. To reduce hot charge carriers, in U.S. Pat. No. 5,134,447, a heterojunction is formed in the vicinity of a pn junction in the body of a MOS transistor.
U.S. Pat. No. 6,531,748 B2 discloses a power component with a MOS structure. The source region in this case is formed of a material that has a lower bandgap than the material of a channel region in order to reduce a current gain of a parasitic bipolar transistor.